1. Field of the Invention
The present invention relates to a light spot position measuring apparatus and a light spot position measuring method, wherein a position or positions of a point light source or point light sources which directly or indirectly emits/emit a light is/are measured using an image pickup device. More specifically, the present invention relates to a technique for measuring the position or positions of the point light source or sources with improved accuracy.
2. Description of the Prior Art
Conventionally, when, for example, measuring a surface configuration of a three-dimensional object, the so-called stereo method has been available, wherein the three-dimensional object to be measured is scanned by a laser beam emitted from a scanning laser projector, and two television cameras are used to capture images of laser-beam spots produced on the three-dimensional object in sequence. Image signals outputted from the television cameras are processed so as to derive three-dimensional positions (coordinates) of the respective laser-beam spots. By synchronously performing the scanning of the three-dimensional object by the laser beam along the surface thereof and the measurement of the three-dimensional coordinates of the respective laserbeam spots in sequence, the surface configuration of the three-dimensional object is measured.
For enhancing the measurement accuracy in the foregoing measuring system, it is necessary to improve the resolution of the television cameras. For the improvement thereof, the number of picture elements (pixels) in the image pickup device such as a CCD image sensor incorporated in the television camera should be greatly increased, which, however, is difficult in view of manufacturing technique.
Technique has been proposed as disclosed in, such as, Japanese Second (examined) Patent Publication No. 3-31362, for improving an apparent or effective resolution of the television camera without increasing the number of the pixels of the image pickup device. According to this technique, a cross filter is mounted to an objective lens of the television camera so as to convert light beams from targets in the form of point light sources (light spots) into cross-shaped streak images through the cross filter. The cross-shaped streak images are projected onto a light-receiving area of the image pickup device. The projected images are processed to derive an intersection point of each cross-shaped streak image for determining a corresponding light spot position, that is, a position of the corresponding point light source forming the target.
However, the foregoing conventional technique has a drawback in that the light source to be used should be capable of emitting a light with a high intensity for enhancing accuracy in detection of the light spot position. Specifically, in the foregoing cross-shaped streak image, roam energy or power of the light is concentrated to the center of the image so that the remaining energy of the light dispersed around a periphery of the image is inevitably small. This means that the light power is not utilized efficiently. As a result, in order to raise the position detection accuracy, the intensity of the light emitted from the light source should be increased. In other words, when an intensity of the light from the light source is lower than a certain level, the cross-shaped streak image is not clearly projected onto the image pickup device, resulting in a problem of poor sensitivity.
Accordingly, when such a conventional technique is applied to the foregoing measurement of the surface configuration of the three-dimensional object or the like, due to limitation of a distance between the television camera and the object and a reflectance on the surface of the object or the like, the application field is inevitably restricted so that, for example, the application to the survey in the civil engineering field or the like is difficult.